Generally, a GaN-based nitride semiconductor is applied to electronic devices that are high-speed switching and high power devices such as optic elements of blue/green LEDs, MESFET, HEMT, etc. In particular, the blue/green LED is under a state in which mass-production has been already progressed and a global sale is being exponentially increased.
The above-mentioned conventional GaN-based nitride semiconductor light emitting device (LED) is grown-up usually on a sapphire substrate or a SiC substrate. Further, at a low growth temperature, an AlyGa1-yN polycrystalline layer is grown-up on the sapphire substrate or the SiC substrate as a buffer layer. After that, at a high temperature, an undoped GaN layer, an n-GaN layer doped with silicon over a 1×1017/cm3 concentration or a combined n-GaN layer thereof is formed on the buffer layer as a first electrode layer. Additionally, on an Mg—AlGaN cladding layer is formed an Mg—GaN layer as a second electrode layer to complete the GaN-based nitride semiconductor LED. Also, a light emitting layer (multi-quantum well active layer) is sandwiched between the first electrode layer and the second electrode layer.
However, the above-constructed conventional nitride semiconductor LED has a crystal defect of a very high value of about 108/cm3 or so, which is generated from an interface between the substrate and the buffer layer.
Accordingly, the conventional nitride semiconductor LED has a drawback in that an electric characteristic, specifically, leakage current under a reverse bias condition is increased, resulting in a fatal influence to the reliability of the device.
Also, the conventional nitride semiconductor LED has another drawback in that the crystal defect generated from the interface between the buffer layer and the substrate deteriorates crystallinity of the light emitting layer thereby lowering the light emitting efficiency.